Technical Field
The present invention relates to corrosion rate computation from corrosion sensors, and more particularly to the real time numerical computation of corrosion rates from a large number of corrosion sensors.
Description of the Related Art
Reactive monitoring of corrosion is based upon measuring a metal film transformation of copper and silver traces as they react with contamination gases. There are many ways to measure the corrosion rate. One way to measure the corrosion rate is to measure the change of electrical resistance for a metal film. A second way to measure the corrosion rate is to measure a frequency shift of a mass balance that has the metal deposited on it. Another way to measure the corrosion rate relies on measuring the mass of a metal coupon before and after exposure to the contaminated atmosphere. The metal film in the above approaches is consumed as the metal is transformed to a corrosion product. In many commercial implementations, there is thus a tradeoff between the lifetime of the sensor and the sensitivity of detection.
Measuring the corrosion rate is based upon determining the slope for the change in metal film thickness over time. If the change in film thickness is significant, the slope can be calculated relatively easily. However, if the change in film thickness is small, a longer time interval should be considered to have a detectable change in film thickness.
The rate of corrosion may vary by an order of magnitude from one location to another in a data center due to spatial and temporal variations, such as air flow, pollutant concentrations, temperature variations, etc. To accurately calculate corrosion rates that may vary from 20 Angstroms (A)/month up to 1000 A/month, the corrosion sensor should be made sensitive enough to pick up small changes in corrosion (the lowest limit is 1 A, which would be a single atom in thickness) and the computation of the corrosion rate should be adaptable to all of the conditions. For conventional corrosion rate computations, such as those based on resistive sensors, temperature and relative humidity variations may lead to inaccurate readings and should be compensated for. At lower corrosion rates (e.g., less than 20 A/month), quantization noise from measurements and temperature measurement noise may also result in inaccurate corrosion rate calculations if the rate is calculated frequently (e.g., every 15 minutes).